Fewer people around Lake Champlain are walking on water than they once did.

Lake Champlain is freezing over less frequently and less extensively than in decades past.

"It's entirely clear the lake isn't freezing over as much as it used to," said Mike Winslow, a staff scientist with the Lake Champlain Committee.

The lack of complete ice cover might be starting to affect the ecology of the lake, and likely has a hand in altering the winter ice-fishing culture on the lake. Ice fishing, a tradition on Lake Champlain for as long as anybody can remember, is shifting away from the increasingly open central part of the lake and north toward sections Lake Champlain that freeze more reliably.

Freeze-up records have been kept for the lake since the early part of the 19th century. The data showed that in each decade from the 1820s through the 1920s, the lake froze every year, or stayed open just once in each 10-year period. The lake failed to close twice in the 1930s, then once in the 1940s.

Since then, freeze-overs are far less likely. In the 1980s and 2000s, the lake froze over in just half the years each decade. In the 1990s, the lake froze completely in just three winters. Lake Champlain has not completely frozen over since March 2007.

A 2010 Nature Conservancy report noted that when the lake does freeze over, it happens on average two weeks later in the winter than it did during the 19th century.

Global warming might be responsible for the lack of recent lake ice, but it's probably not the whole story. Ice cover began diminishing in the 1950s, before there was a marked increase in winter temperatures in the Champlain Valley. Observers say part of the reason for the fewer reported number of years with solid ice on the lake is that small gaps in the ice are more visible from airplanes than they are from shore.

Other issues besides warm winters conceivably could be at work, said James Ehlers of Lake Champlain International. He wondered if treated wastewater is warmer than water that would normally flow into the lake. And stormwater flowing over pavement is warmer than it otherwise would be, he said. Is that warmer water having any effect on lake ice, or is it too small of an amount to make a difference? Ehlers said he doesn't know, but it would be interesting to learn.

In any event, the ice unquestionably is important to sportspeople on the lake. A 2010 Fish and Wildlife Department anglers' survey indicates 19,000 of the state's 75,000 anglers ice-fished on Lake Champlain in 2009. About 2,900 people from out-of-state also ice-fished on Lake Champlain, according to the survey.

Ecological impact

It's unclear whether the lack of ice on Lake Champlain has had any effects on the local environment. Nobody has noticed anything major, Winslow said. Many other lakes in the Northern Hemisphere also are freezing less completely than they used to as the climate warms. A bit of data can be gleaned from those bodies of water, Winslow said.

Studies from German lakes indicate that less ice causes plankton to grow at different times than in the past. Plankton is a basic food in a lake ecosystem, and fish are a big consumer of plankton.

That could lead to problems if the spawning schedule of fish gets out of sync with plankton growth, Winslow said.

Scientists still are trying to determine how less ice would affect a variety of species. Perhaps alewives, which is considered a nuisance species in Lake Champlain, might be harmed by less ice cover. Another invasive pest, milfoil, might germinate at different times, but what effect that would have on the overall population of the nuisance plant is unknown, Winslow said.

Cold-water fish, such as trout, Atlantic salmon and whitefish, probably won't suffer at all with less ice, said Brian Chipman, a fisheries biologist at the Vermont Department of Fish and Wildlife. The lake is immense, with plenty of deep, cold water for these species regardless of whether the lake freezes.

However, the Nature Conservancy report disagrees, saying there is the potential for harm to cold-water fish if ice continues to diminish, because they might not be able to adapt quickly enough to changing water temperatures or ice cover.

Overall, it might be hard to tease out effects caused by a lack of lake ice or other factors, such as warmer water temperatures.

The lack of ice is affecting only parts of Lake Champlain. The northern end of the lake is, for the most part, rather shallow and regularly freezes over completely. The freeze-over in the bays near the northern Champlain Islands was late this year — around Christmas — but a foot of ice now covers several bays and inlets near Alburgh and North Hero.

The culture

The broad lake, off Burlington, is wide open, which is an increasingly common occurrence. In some of those years, Burlington's inner harbor, from the shore to the breakwater, would freeze, but not every year. The result: The throngs of people often seen strolling on the ice inside the breakwater on nice winter days is a less common sight.

In recent decades, the lake also has started to stay open farther south, near Thompson's Point, said Bruce Chipman, a fisheries biologist with the Vermont Department of Fish and Wildlife.

Although there's been little discernable ecological effect of the scant ice near Thompson's Point, there's a lot less ice fishing off of southern Chittenden and northern Addison counties.

Leo Collins, 84, of Berkshire says he has fond memories of ice fishing near Thompson's Point off Charlotte and Long Point off neighboring Ferrisburgh in the 1940s. "We used to go down below Charlotte, go out and fish for smelt," he said.

"Back in the 1940s, there were quite a lot of fishermen. We used to go down there, and it would be like a little village. A good get-together. They'd visit and come out of their shanties and visit and ask how the fish were biting," Collins said.

When the ice was good near Charlotte, usually from mid January until the end of February, there would be a little village of roughly a dozen shanties.

Collins said he stopped ice fishing several years ago because age caught up with him, and he worried a slip and fall would be catastrophic.

With so much less ice near Thompson's Point, Collins said he imagines smelt fishing has taken a dive. People have no doubt retreated north to the Champlain Islands, where there's plenty of lake perch but not much smelt, Collins said.

Chipman said there's a change in behavior among ice-fishing enthusiasts, he said. They're migrating north, to where they still can walk on water.

The north

One recent afternoon, the bays around Alburgh and North Hero had ice at least a foot thick, and a number of ice-fishing enthusiasts were out in bright sunshine and a chilly south wind.

The lack of snow so far this winter exposed most of the hard, clear ice covering the bays and inlets in the Champlain Islands. Sun glared off the rough surface, making the lake resemble a photograph of small ripples on water stirred up by the wind. A few small, lonely snow drifts, the legacy of a brief snow squall last week, were scattered near the shore like timid swimmers wading into cold water.

Roger and Ann Davis of Danielsville, Pa., said they spent most of the week in North Hero, ensconced in a fishing shanty about 40 feet off shore, their car parked conveniently next to it — atop solid ice about a foot thick.

Lake Champlain attracted the pair because bodies of water near their home aren't freezing. It's been too warm in Pennsylvania, Roger Davis said. "It's not frozen where we are," he said. "We're chasing the ice."

The couple said they were planning to pack up and head north into Canada for more ice fishing.

As the Davises kept catching small perch, Chris Wright, 41, of Alburgh was about a half a mile north, unprotected by a shanty, also seeking perch. He said his catch Thursday was, at best, so-so.

Wright, bundled beneath layer upon layer of clothes to shield against moderate wind gusts, said he ice fishes at least five times a week. He remarked how few people there were on the lake.

It probably wasn't a lack of ice, he said. After all, he was standing on plenty of it. He attributed the decline to reasons such as high gas prices, which discourage people from driving to the lake, and young people who are less inclined to ice fish than their parents.

"Young kids, for the most part, don't do this as much. They're at the computer all the time," Wright said. "When I was a teen, that's all we did: hunt and fish."

Chipman said if the culture of ice fishing on the lake is changing, a lack of ice on parts of the lake is only a part of the reason why. Modern technology, such as portable, collapsible shanties, make coming and going easier.

"Those more-or-less permanent shanty towns are not as prevalent as they used to be. The portable shanties might make it less likely for little communities to spring up in any one location in the winter," Chipman said

He doesn't see an end to ice fishing any time soon. If one part of the lake is open, there's plenty of other areas to go. "What a lot of people are finding is, you'll get a lot more fish if you're willing to wander," Chipman said.

And overall fish numbers and health in Lake Champlain are robust, Chipman added.

Vast areas of Lake Champlain remain ice-free. Warm weather expected early this week would prevent much additional freezing. But it's anyone's guess as to whether the lake will freeze entirely this winter. A cold February still could lock in the lake, Winslow said.